In a typical cellular radio system, wireless terminals (also known as mobile stations and/or user equipment units (UEs)) communicate via a radio access network (RAN) to one or more core networks. The wireless terminals can be mobile stations or user equipment units (UE) such as mobile telephones (“cellular” telephones) and laptops with wireless capability (e.g., mobile termination), and thus can be, for example, portable, pocket, hand-held, computer-included, or car-mounted mobile devices which communicate voice and/or data with the radio access network.
The radio access network (RAN) covers a geographical area which is divided into cell areas, with each cell area being served by a base station, e.g., a radio base station (RBS), which in some networks is also called “NodeB” or “B node”. A cell is a geographical area where radio coverage is provided by the radio base station equipment at a base station site. Each cell is identified by an identity within the local radio area, which is broadcast in the cell. The base stations communicate over the air interface operating on radio frequencies with the user equipment units (UE) within range of the base stations.
In some versions of the radio access network, several base stations are typically connected (e.g., by landlines or microwave) to a radio network controller (RNC). The radio network controller, also sometimes termed a base station controller (BSC), supervises and coordinates various activities of the plural base stations connected thereto. The radio network controllers are typically connected to one or more core networks.
The Universal Mobile Telecommunications System (UMTS) is a third generation mobile communication system, which evolved from the Global System for Mobile Communications (GSM), and is intended to provide improved mobile communication services based on Wideband Code Division Multiple Access (WCDMA) access technology. UTRAN, short for UMTS Terrestrial Radio Access Network, is a collective term for the Node B's and Radio Network Controllers which make up the UMTS radio access network. Thus, UTRAN is essentially a radio access network using wideband code division multiple access for user equipment units (UEs).
In a forum known as the Third Generation Partnership Project (3GPP), telecommunications suppliers propose and agree upon standards for third generation networks and UTRAN specifically, and investigate enhanced data rate and radio capacity. The Third Generation Partnership Project (3GPP) has undertaken to evolve further the UTRAN and GSM based radio access network technologies. In this regard, specifications for the Evolved Universal Terrestrial Radio Access Network (E-UTRAN) are ongoing within the 3rd Generation Partnership Project (3GPP). The Evolved Universal Terrestrial Radio Access Network (E-UTRAN) comprises the Long Term Evolution (LTE) and System Architecture Evolution (SAE).
Long Term Evolution (LTE) is a variant of a 3GPP radio access technology wherein the radio base station nodes are connected directly to a core network rather than to radio network controller (RNC) nodes. In general, in LTE the functions of a radio network controller (RNC) node are performed by the radio base stations nodes. As such, the radio access network (RAN) of an LTE system has an essentially “flat” architecture comprising radio base station nodes without reporting to radio network controller (RNC) nodes.
The Long Term Evolution (LTE) standard is based on multi-carrier based radio access schemes such as Orthogonal Frequency-Division Multiplexing (OFDM) in the downlink and SC-FDMA in the uplink. The Orthogonal FDM's (OFDM) spread spectrum technique distributes the data over a large number of carriers that are spaced apart at precise frequencies. This spacing provides the “orthogonality” in this technique which prevents the demodulators from seeing frequencies other than their own. The benefits of OFDM are high spectral efficiency, resiliency to RF interference, and lower multi-path distortion.
In LTE a frame having both downlink portion(s) and uplink portion(s) is communicated between the base station and the wireless terminal. Each LTE frame can comprise plural subframes. In the time domain, each LTE subframe (having 1 ms duration) is divided into two slots, each slot being 0.5 ms in duration. The transmitted signal in each slot is described by a resource grid of subcarriers and symbols. Each element in the resource grid is called a resource element (RE) and is uniquely defined by an index pair (k,l) in a slot (where k and l are the indices in the frequency and time domain, respectively). In other words, one symbol on one sub-carrier is a resource element (RE). Each symbol thus comprises a number of sub-carriers in the frequency domain, depending on the channel bandwidth and configuration. The smallest time-frequency resource supported by the standard today is a set of plural subcarriers and plural symbols (e.g., plural resource elements (RE)) and is called a resource block (RB) (e.g. 12 subcarriers and 7 symbols) See, e.g., 3GPP TS 36.211 V8.5.0 (2008-12) section 5.2.
In Long Term Evolution (LTE) no dedicated data channels are used, instead shared channel resources are used in both downlink and uplink. These shared resources, e.g., the downlink shared channel (DL-SCH) and the uplink shared channel (UL-SCH) are each controlled by one or more schedulers that assign(s) different parts of the downlink and uplink shared channels to different UEs for reception and transmission respectively. The assignments for the downlink shared channel (DL-SCH) and the uplink shared channel (UL-SCH) are transmitted in a control region covering a few OFDM symbols in the beginning of each downlink subframe.
FIG. 1 illustrates some of the foregoing in simplified fashion by showing that, in Long Term Evolution (LTE), the total bandwidth of the carrier is divided into several sub-bands and the time domain is divided into time slots. This gives a grid of time-frequency blocks, e.g., the aforementioned resource blocks (RB). In each time slot, users are scheduled to one or several sub-bands. FIG. 2 shows users scheduled to different sub-bands in one time slot. In the uplink, when plural sub-bands are scheduled for a same user, the plural sub-bands have to be consecutive. Users in adjacent and neighboring cells can be allocated to the same sub-band in the same time slot, and therefore can interfere with each other.
The nature and number of mobile broadband communications are greatly increasing. Moreover, mobile broadband communications largely happens indoors. By “indoors” is meant that wireless terminals which participate in the mobile broadband communications, though wireless, are typically situated within some type of structure (e.g., building or vehicle) during at least a portion of the broadband session. For example, most users surf the internet from their personal computer (PC) or laptop, which generally are located indoors at the time of the communications session. It is natural that these types of wireless terminals be in homes and/or buildings. Some network operators have reported that up to 50-80% of their users are indoor users.
In the uplink, the operating power for a wireless terminal (e.g., user equipment unit (UE)) is limited from the outset (e.g., is not as great as downlink transmission power from the base station). The relatively low power signal emanating from an indoor wireless terminal is reduced further by a loss factor occasioned by the structure or building in which an indoor wireless terminal is located.
To make matters worse, the signal emanating from an indoor wireless terminal can be interfered with by other users. If the other users are outdoor users, those outdoor users may have stronger signal since, unlike the indoor user, the outdoor user signal is not reduced by building loss.
In view of factors such as those mentioned above, the indoor user could well have poor performance, particularly in the uplink. In the downlink, the problem is typically not as severe. In the downlink the base station has more power and the interference situation is different, since downlink interference is shielded by the building for the indoor user.
Thus, due to such factors as high building losses, indoor users have generally higher pathloss than outdoor users in the uplink (UL) to the serving cell and probably also higher pathloss to surrounding cells. Therefore the indoor users will create less interference than outdoor users in the uplink.
In existing solutions, indoor and outdoor users are scheduled randomly in the frequency- and time-domain. It is therefore entirely possible that an indoor user can be scheduled on a same time slot and on a same sub-band as an outdoor user. In such case, the indoor users will experience a high interference level which will possibly give an undesirably low bitrate.